英文:
Passing []*io.PipeWriter to io.MultiWriter
问题
我有一堆创建的*io.PipeWriter，想要在一个函数中基于所有这些pipewriter创建一个multiwriter。所以我调用一个函数，类似这样：
func copyToWriters(reader *bufio.Reader, errs chan error, writers []*io.PipeWriter) {
for _, writer := range writers {
defer writer.Close()
}
mw := io.MultiWriter(writers)
_, err := io.Copy(mw, reader)
if err != nil {
errs <- err
}
}
我使用参数copyToWriters(reader, errs, []*io.PipeWriter{w1, w2})调用该方法。
但是它报错说cannot use writers (type []*io.PipeWriter) as type []io.Writer in argument to io.MultiWriter。但是如果我将io.MultiWriter(writers)改为io.MultiWriter(writers[0],writers[1])，它就可以工作了。我该如何使现有的函数能够正常工作，而不必单独传递writers呢？
英文:
I have a bunch of *io.PipeWriter created and would like to make a multiwriter based on all those pipewriters in a function. So I call a function something like
func copyToWriters(reader *bufio.Reader, errs chan error, writers []*io.PipeWriter) {
for _, writer := range writers {
defer writer.Close()
}
mw := io.MultiWriter(writers)
_, err := io.Copy(mw, reader)
if err != nil {
errs <- err
}
}
I call the method with arguments copyToWriters(reader, errs, []*io.PipeWriter{w1, w2})
But it says
cannot use writers (type []*io.PipeWriter) as type []io.Writer in argument to io.MultiWriter. But
if I change io.MultiWriter(writers) to io.MultiWriter(writers[0],writers[1]) it works. How can I make the existing function work by not having to pass writers separately.
答案1
得分: 5
很抱歉，Golang的类型系统不允许将[]*io.PipeWriter强制转换为[]io.Writer，即使*io.PipeWriter实现了io.Writer接口，因为这需要O(n)的操作（参考链接：https://stackoverflow.com/questions/12753805/type-converting-slices-of-interfaces-in-go/12754757#12754757）。
你能做的最好的办法是创建另一个[]io.Writer并将管道写入器复制到其中：
ws := make([]io.Writer, len(writers))
for i, w := range writers {
ws[i] = w
}
mw := io.MultiWriter(ws...)
关于为什么需要使用...，请阅读文档（链接：https://golang.org/ref/spec#Passing_arguments_to_..._parameters）。
英文:
Unfortunately, Golang's type system does not allow casting []*io.PipeWriter to []io.Writer even when *io.PipeWriter implements io.Writer since it requires O(n) operation (reference).
The best you can do is create another []io.Writer and copy the pipe writers into it
ws := make([]io.Writer, len(writers))
for i, w := range writers {
ws[i] = w
}
mw := io.MultiWriter(ws...)
And reason why you nead ..., read the document
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